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ORIGINAL ARTICLE

Evaluation of the root and root canal

systems of mandibular first premolars in

northern Taiwanese patients using

cone-beam computed tomography

Yao-Der Huang

a,b

, Jay Wu

b,c

, Rong-Jiun Sheu

b

,

Mu-Hsiung Chen

a

, Der-Lan Chien

a

, Ya-Ting Huang

a

,

Chih-Chia Huang

a,d

, Yunn-Jy Chen

a,e,

*

a

Department of Dentistry, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan

bInstitute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu, Taiwan c

Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung, Taiwan

d

Department of Dentistry, Cardinal Tien Hospital, New Taipei City, Taiwan

eSchool of Dentistry, National Taiwan University, Taipei, Taiwan

Received 29 April 2014; received in revised form 17 May 2014; accepted 22 May 2014

KEYWORDS

cone-beam computed tomography; mandibular first

premolar; root canal system; Taiwanese

Background/Purpose: Cone-beam computed tomography (CBCT) can provide valuable data for root canal systems of human teeth in vivo. This study used CBCT to evaluate the number of roots and canals of 300 mandibular first premolars in 150 northern Taiwanese patients. Methods: The root canal systems of 300 mandibular first premolars in 150 northern Taiwanese patients with bilateral premolars were analyzed by CBCT.

Results: Of the 300 mandibular first premolars, 197 (65.7%) had one root with one canal (1R1C), 49 (16.3%) had one root with two canals (1R2C), 51 (17.0%) had two roots with one ca-nal in each root (2R2C), and three (1.0%) had three roots with one caca-nal in each root (3R3C). Statistical analyses showed that women had a significantly higher incidence of 1R1C mandib-ular first premolars (71.4%) than men (58.8%, pZ 0.031), and men had a significantly higher incidence of 2R2C mandibular first premolars (27.2%) than women (8.5%, p< 0.001). One hun-dred and twenty-two (81.3%) of the 150 patients had a symmetrical root and root canal system between the right and left mandibular first premolars. Men had a significantly higher symmet-rical rate of 2R2C mandibular first premolars (26.5%) than women (8.2%, pZ 0.013).

Conflicts of interest: All contributing authors declare no conflicts of interest.

* Corresponding author. Department of Dentistry, National Taiwan University Hospital, College of Medicine, National Taiwan University, Number 1, Chang-Te Street, Taipei 10048, Taiwan.

E-mail address:chenyj@ntu.edu.tw(Y.-J. Chen).

http://dx.doi.org/10.1016/j.jfma.2014.05.008

0929-6646/Copyrightª 2014, Elsevier Taiwan LLC & Formosan Medical Association. All rights reserved.

Available online atwww.sciencedirect.com

ScienceDirect

journal homepage: www. jfma-online. com

Journal of the Formosan Medical Association (2015) 114, 1129e1134 Provided by Elsevier - Publisher Connector

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Conclusion: Approximately 82% of mandibular first premolars in northern Taiwanese patients have one root with either one or two canals. There are significant differences in the number of roots and canals and symmetry of the root canal system of bilateral mandibular first premo-lars between male and female northern Taiwanese patients.

Copyrightª 2014, Elsevier Taiwan LLC & Formosan Medical Association. All rights reserved.

Introduction

The success of nonsurgical root canal therapy (NSRCT) is dependent on thorough biomechanical instrumentation, effective chemical debridement, and hermetic obturation of the root canal system. To achieve these goals, a com-plete knowledge of basic root canal morphology and its variation is absolutely necessary for every dentist before performing the endodontic treatment. Incorrect identifi-cation of the number of roots and root canals usually results in endodontic treatment failure.

A previous study at the University of Washington found that the mandibular first premolar has the highest failure rate of 11.45% among all teeth after NSRCT.1 This high

failure rate is probably due to the numerous variations in the root and root canal system of the mandibular first premolars. Several factors that contributed to variations in the root and root canal system of the mandibular first premolar have been reported.2 These factors include ethnicity, age, sex, unintentional bias in selection of clin-ical examples of teeth (specialty endodontic practice vs. general dental practice), and study design (in vitro vs. in vivo).2

The mandibular first premolar is typically of a single-rooted tooth, but two-single-rooted, three-single-rooted, and four-rooted varieties of the mandibular first premolars have also been reported.2e17The root and root canal systems of the mandibular first premolars have been evaluated in different races by different identification methods in several studies.2e17 Most of these studies used samples of

extracted teeth that were examined by clearing,3e9 sectioning,10,11 or radiographic methods.12e14 Only a few

previous studies used cone-beam computed tomography (CBCT) to examine the root and root canal systems of the mandibular first premolars in vivo.15e17 The high failure rate of NSRCT for mandibular first premolars indicates the urgent need to study the complicated root and root canal systems of the mandibular first premolars. In addition, the root canal morphology of the mandibular first premolars in Taiwanese patients has not been investigated. Therefore, this study used CBCT to evaluate the number of roots and root canals of 300 mandibular first premolars in 150 northern Taiwanese patients.

Materials and methods

CBCT images of 500 patients aged 12e95 years were retrieved from the files of the Department of Dentistry, National Taiwan University Hospital, Taipei, Taiwan from November 2011 to March 2013. These patients were scheduled for examination by CBCT (i-CAT; Imaging Sci-ences International, Hatfield, PA, USA) before dental

implantation, or orthodontic, endodontic, or periodontal treatment. The CBCT machine used for tooth identification in this study produced isotropic voxels with a size of 0.25e0.4 mm, resulting in a mean resolution of 0.25 mm. After obtaining informed consent from each patient, a 20e40-second, 120-kV, 3e7-mA, 6e22-cm height CBCT scan was taken. All CBCT images of 500 patients were initially examined and only patients with intact and fully erupted bilateral permanent mandibular first premolars showing completely formed root apices were included. Permanent mandibular first premolars that had shifted mesially or distally due to early loss of adjacent teeth were excluded. Moreover, mandibular first premolars with root canal ther-apy, posts in root canals, or crown restorations were also excluded. According to the aforementioned inclusion and exclusion criteria, 150 patients (68 men and 82 women) with a total of 300 mandibular first premolars were included in this study. This study was approved by the Institutional Review Board of National Taiwan University Hospital.

All CBCT images were then reconstructed by the i-CAT Image System and the images were displayed on a 20-in, flat-panel, medical liquid crystal display (EIZO FlexScan S2000, Hakusan, Ishikawa, Japan) at 1600 1200 lines, with a resolution of 0.08 mm. Each image reconstruction process required approximately 2 minutes. Cross-sectional images through the mandibular first premolars were obtained and analyzed by two endodontists and one radiologist to determine the number of roots and canals of each mandibular first premolar. Disagreement in the identifica-tion of root and root canal numbers was further discussed until a consensus was reached.

The differences in incidences of the root and root canal systems of mandibular first premolars among the four different types and between any two types were analyzed statistically by Chi-square test between two different age groups ( or <50 years) of patients, between men and women, and between left and right mandibular first pre-molars. In addition, the differences in the symmetrical rate of the root and root canal system of bilateral mandibular first premolars in 150 northern Taiwanese patients among four different types and between any two types of the root and root canal system were analyzed statistically by Chi-square test between two different age groups ( or <50 years) of patients and between men and women.

Results

After a detailed examination of the root and root canal systems of all 300 mandibular first premolars, four types of the root and root canal systems, including one root with one canal (1R1C), one root with two canals (1R2C), two

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roots with one canal in each root (2R2C), and three roots with one canal in each root (3R3C), were identified (Fig. 1). In this study, the 1R1C included the type I root canal system (single root canal leaves the pulp chamber and ends as single foramen) of the Vertucci’s classification.3Moreover, the 1R2C included the type II (two root canals leave the pulp chamber and end as single foramen) and type III (single root canal leaves the pulp chamber, separates into two separate root canals, and ends as single foramen) root canal systems.3 The 2R2C included the type IV (two root

canals leave the pulp chamber and end as two foramina), type V (single root canal leaves the pulp chamber and ends as two foramina), type VI (two root canals leave the pulp chamber, join again as single root canal, and end as two foramina), and type VII (single root canal leaves the pulp chamber and separates into two separate root canals, which join again as a single root canal and end as two foramina) root canal systems.3The 3R3C included the type VIII root canal system (three root canals leave the pulp chamber and end as three foramina) of the Vertucci’s classification.3

Of the 300 mandibular first premolars, 197 (65.7%) had 1R1C, 49 (16.3%) had 1R2C, 51 (17.0%) had 2R2C, and three (1.0%) had 3R3C (Table 1). There was a significant differ-ence in the root and root canal system of mandibular first premolars between male and female patients (p< 0.001). Women had a significantly higher incidence of 1R1C mandibular first premolars (71.4%) than men (58.8%,

pZ 0.031), and a marginally significantly higher incidence of 1R2C mandibular first premolars (20.1%) than men (11.8%, p Z 0.073). By contrast, men had a significantly higher incidence of 2R2C mandibular first premolars (27.2%) than women (8.5%, p < 0.001). However, no significant difference in the root and root canal system of the mandibular first premolars was found between patients50 years of age and patients<50 years of age (p Z 0.480) as well as between the left and right teeth (pZ 0.815;Table 1).

One hundred and twenty-two (81.3%) of the 150 pa-tients had a symmetrical root and root canal system be-tween the right and left mandibular first premolars. Of these 122 patients with symmetrical bilateral mandibular first premolars, 88 (72.1%) had 1R1C premolars, 14 (11.5%) had 1R2C premolars, 19 (15.6%) had 2R2C premolars, and one (0.8%) had 3R3C premolars (Table 2). There was a significant difference in the symmetrical rate of mandib-ular first premolars between male and female patients (pZ 0.009). Women had a marginally significantly higher symmetrical rate of 1R2C mandibular first premolars (16.4%) than men (4.1%, pZ 0.070). By contrast, men had a significantly higher symmetrical rate of 2R2C mandibular first premolars (26.5%) than women (8.2%, p Z 0.013). However, no significant difference in the symmetrical rate of mandibular first premolars was found between patients  50 years of age and patients <50 years of age (pZ 0.892;Table 2).

Figure 1 Cone-beam computed tomography images of mandibular first premolars showing four different types of root canal system. (A) Bilateral mandibular first premolars with a symmetrical one root with one canal (1R1C) root canal system; (B) bilateral mandibular first premolars with a symmetrical one root with two canals (1R2C) root canal system; (C) bilateral mandibular first premolars with a symmetrical two roots with one canal in each root (2R2C) root canal system; and (D) bilateral mandibular first premolars with a symmetrical three roots with one canal in each root (3R3C) root canal system.

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Discussion

The root and root canal systems of the mandibular first premolars can be assessed by both in vitro and in vivo techniques (Table 3).3e17In vitro techniques are clearing, sectioning, and radiographic methods, and these tech-niques use extracted teeth for analyses of the numbers of roots and root canals.3e14 For the clearing method, the

extracted teeth are accessed, pulp tissues are removed, and the root canal systems are stained with India ink. The teeth are rendered clear by demineralization and immer-sion in methyl salicylate. The root and root canal systems of the cleared teeth are then examined and recorded.3e9For

the sectioning method, the roots of extracted teeth are sectioned at different levels perpendicular to the long axis. The resected root surfaces are polished, rinsed, dried, stained with methylene blue, and photographed for evalu-ation of the root and root canal systems.10,11 For radio-graphic method, the root and root canal systems of the extracted teeth are evaluated by multislice CT or

micro-CT.12e14Because the in vitro techniques evaluate only the extracted teeth, they are not masked by other structures and thus are more accurate to identify the number of roots and canals in a tooth. However, they are time consuming due to involvement of many procedures to prepare the teeth for examination. For the in vivo techniques, teeth in situ are examined by periapical radiography, conventional CT, or CBCT.15e17Because the roots and root canals of the teeth may be obscured by the surrounding structures when taking the radiographs, the images of teeth may not be sharp enough for examining the details of the root and root canal systems of the teeth.

Recently, CBCT was used as the major technique for studying the root and root canal systems of human teeth in vivo.15e17The distinct advantage of CT is that it allows for three-dimensional (3D) reconstruction of the root and root canal systems of the teeth. CT has been suggested as the preferential imaging modality in difficult situations demanding localization and description of the root and root canal systems because of its ability to render 3D

Table 1 Four different types of the root and root canal system for the 300 mandibular first premolars in 150 Taiwanese patients according to the age and sex of the patients and tooth side.

Total tooth number

Root and root canal system of mandibular first premolars (tooth number/percentage) p (Chi-square test) 1R1C 1R2C 2R2C 3R3C Age (y) 0.480 50 130 90 (69.2) 19 (14.6) 21 (16.2) 0 (0.0) <50 170 107 (63.0) 30 (17.6) 30 (17.6) 3 (1.8) Sex <0.001 Men 136 80 (58.8) 16 (11.8) 37 (27.2) 3 (2.2) Women 164 117 (71.4) 33 (20.1) 14 (8.5) 0 (0.0) Side 0.815 Left 150 94 (62.7) 26 (17.3) 29 (19.3) 1 (0.7) Right 150 103 (68.7) 23 (15.3) 22 (14.7) 2 (1.3) Total 300 197 (65.7) 49 (16.3) 51 (17.0) 3 (1.0)

1R1CZ one root with one canal; 1R2C Z one root with two canals; 2R2C Z two roots with one canal in each root; 3R3C Z three roots with one canal in each root.

Table 2 Symmetry of the root and root canal system between the right and left mandibular first premolars in 150 Taiwanese patients according to the age and sex of the patients.

Patient with symmetry of the root and

root canal system of mandibular first premolars (patient number/percentage)

P (Chi-square test) Total 1R1C 1R2C 2R2C 3R3C Age (y) 0.892 50 55 42 (76.4) 5 (9.1) 8 (14.5) 0 (0.0) <50 67 46 (68.7) 9 (13.4) 11 (16.4) 1 (1.5) Sex 0.009 Men 49 33 (67.4) 2 (4.1) 13 (26.5) 1 (2.0) Women 73 55 (75.4) 12 (16.4) 6 (8.2) 0 (0.0) Total 122 88 (72.1) 14 (11.5) 19 (15.6) 1 (0.8)

1R1CZ one root with one canal; 1R2C Z one root with two canals; 2R2C Z two roots with one canal in each root; 3R3C Z three roots with one canal in each root.

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information.18 Moreover, CBCT uses an extraoral imaging scanner to produce 3D scans of the maxillofacial skeleton at a considerably lower radiation dose than conventional CT. Neelakantan et al18 compared the accuracy of several

techniques in studying the root and root canal morphology of extracted human teeth. When modified canal staining and clearing technique was used as the gold standard, they found that CBCT and peripheral quantitative CT are as ac-curate as the gold standard in identifying root canal sys-tems. In addition, CBCT was shown to be more accurate than spiral CT and plain and contrast medium-enhanced digital radiography in studying the root canal morphology of teeth.18Because CBCT can provide 3D information of the

teeth and jaw bones and needs only a lower radiation dose to produce a high-quality image, CBCT has been considered to be as an excellent tool for investigation of root canal morphology of teeth as well as diagnosis and preoperative assessment of the diseased teeth or jaw bones in daily dental practice.15e19

This study found four types of root and root canal sys-tems in mandibular first premolars, of which 1R1C (65.7%) was the most common type, followed by the 2R2C (17.0%), 1R2C (16.3%), and 3R3C (1%) types. All previous studies agreed that 1R1C is the most common type of the root and canal system in mandibular first premolars with the in-cidences varying from 58.2% to 88.5% (Table 3).3e17 More-over, the majority of the previous and present studies also agreed that 2R2C is the second common type with the in-cidences ranging from 8.2% to 33%,3,4,6e10,14e17and 1R2C is

the third common type with the incidences ranging from 0% to 16.3%.3,4,6e10,16,17 By contrast, some of the previous

studies showed that 1R2C is the second common type with the incidences ranging from 12% to 29%,5,12,13and 2R2C is

the third common type with the incidences ranging from 3.6% to 9.5%.5,12,13The incidences of 3R3C plus other types

of the root and root canal systems in mandibular first pre-molars are usually equal to or less than 6% with only one exception showing the incidence of 8.7% for the other types of the root and canal system in mandibular first premolars (Table 3).3e17 The discrepancies in the results of present and previous studies were probably due to collection of sample teeth from different races, ages, and sexes, unin-tentional bias in selection of clinical examples of teeth (specialty endodontic practice vs. general dental practice), and study design (in vitro vs. in vivo).2e17However, when CBCT is used to study the root and canal systems of mandibular first premolars in Chinese and Taiwanese pa-tients, a similar tendency is found with the 1R1C, 2R2C, 1R2C, and 3R3C plus other types being the first, second, third, and fourth common types of the root and canal sys-tem in mandibular first premolars, respectively.16,17

This study found a significant difference in the root and root canal system of mandibular first premolars between male and female Taiwanese patients. Women had a signif-icantly higher incidence of 1R1C mandibular first premolars (71.4%) than men (58.8%, p Z 0.031), but men had a significantly higher incidence of 2R2C mandibular first premolars (27.2%) than women (8.5%, p< 0.001). A similar finding showing a significant sex difference in the root canal morphology of mandibular first premolars was reported by Sert and Bayirli.5They found two or more canals in 44% of women and 35% of men in a Turkish population. However,

Table 3 Number of roots and canals of mandibular first premolars in different reported populations (incidence by number of teeth).

Methods of study References Year Nation Total teeth studied

1R1C 1R2C 2R2C 3R3C Other

types Type Ia Types II and IIIa

Types IVeVIIa Type VIIIa

In vitro; clearing Vertucci3 1984 USA 400 70% (280) 4% (16) 25.5% (102) 0 0.5% (2) Calis‚kan et al4 1995 Turkey 100 64% (64) 11% (11) 19% (19) 6% (6) 0% (0)

Sert and Bayirli5 2004 Turkey 200 60.5% (121) 29% (58) 9.5% (19) 1% (2) 0% (0) Rahimi et al6 2007 Iran 163 69.4% (113) 5.5% (9) 23.9% (39) 0% (0) 1.2% (2) Awawdeh and Al-Qudah7 2008 Jordan 500 58.2% (251) 36.2% (31) 33% (165) 0% (0) 2.6% (13) Velmurugan and Sandhya8 2009 India 100 72% (72) 9% (9) 18% (18) 0% (0) 1% (1) Jain and Bahuguna9 2011 India 138 67.4% (93) 11.6% (16) 21.0% (29) 0% (0) 0% (0) In vitro; sectioning Baisden et al10 1992 USA 106 76% (80) 0% (0) 24% (26) 0% (0) 0% (0) Khedmat et al11 2010 Iran 217 88.5% (192) 5.1% (11) 5.1% (11) 0% (0) 1.4% (3)

In vitro; MSCT Sikri and Sikri12 1994 India 112 70.5% (79) 25.9% (29) 3.6% (4) 0% (0) 0% (0) Sandhya et al13 2010 India 100 80% (80) 12% (12) 6% (6) 0% (0) 2% (2) In vitro; micro-CT In vivo; CBCT Liu et al14 Liao et al15 2013 2011 China China 115 97 65.2% (75) 83.5% (81) 2.6% (3) 3.1% (3) 23.5% (27) 8.2% (8) 0% (0) 0% (0) 8.7% (10) 5.2% (5) Yu et al16 2012 China 178 86.8% (151) 1.7% (3) 9.8% (17) 0.6% (1) 1.1% (2) Yang et al17 2013 China 440 76.1% (335) 6.1% (27) 15.9% (70) 0.7% (3) 1.1% (5)

Present study 2014 Taiwan 300 65.7% (197) 16.3% (49) 17.0% (51) 1.0% (3) 0% (0) 1R1CZ one root with one canal; 1R2C Z one root with two canals; 2R2C Z two roots with one canal in each root; 3R3C Z three roots with one canal in each root; CBCTZ cone-beam computed tomography; micro-CT Z micro-computed tomography; MSCT Z multislice computed tomography.

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most other root and root canal investigations did not pay a special attention to compare the difference in the root and root canal systems of mandibular first premolars between male and female patients studied.2e17

Symmetry of the root and root canal morphology be-tween bilateral teeth in a same patient is rarely studied. Plotino et al20investigated symmetry of root and root canal morphology of bilateral maxillary and mandibular molars in a white population by CBCT. They found that the symmet-rical rate is 71.1% for maxillary first molars, 79.6% for maxillary second molars, 70.6% for mandibular first molars, and 81% for mandibular second molars.20 This study demonstrated a symmetrical rate of 81.3% for mandibular first premolars in 150 northern Taiwanese patients. Sym-metry of root and root canal morphology between bilateral mandibular first premolars has not been reported in previ-ous studies.2e17

In this study, we used CBCT to study 300 mandibular first premolars in 150 northern Taiwanese patients. We found that 65.7% of 300 mandibular first premolars had 1R1C, 17.0% had 2R2C, 16.3% had 1R2C, and 1.0% had 3R3C. Women had a significantly higher incidence of 1R1C mandibular first premolars (71.4%) than men (58.8%), and men had a significantly higher incidence of 2R2C mandib-ular first premolars (27.2%) than women (8.5%). A total of 122 (81.3%) of the 150 patients had a symmetrical root and root canal system between the right and left mandibular first premolars. Men had a significantly higher symmetrical rate of 2R2C mandibular first premolars (26.5%) than women (8.2%). We conclude that approximately 82% of mandibular first premolars in northern Taiwanese patients have one root with either one or two canals. There are significant differences in the number of roots and root ca-nals as well as in symmetry of the root and root canal sys-tem of bilateral mandibular first premolars between male and female northern Taiwanese patients.

Acknowledgments

The authors acknowledge statistical assistance provided by the Taiwan Clinical Trial Bioinformatics and Statistical Center, Training Center, and Pharmacogenomics Laboratory.

References

1.Ingle J, Bakland I. Endodontics. 5th ed. Hamilton, Ontario, Canada: BC Decker; 2002.

2.Cleghorn BM, Christie WH, Dong CC. The root and root canal morphology of the human mandibular first premolar: a litera-ture review. J Endod 2007;33:509e16.

3.Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Pathol 1984;58:589e99.

4. Calis‚kan MK, Pehlivan Y, Sepetc¸ioglu F, Tu¨rku¨n M, Tuncer SS. Root canal morphology of human permanent teeth in a Turkish population. J Endod 1995;21:200e4.

5. Sert S, Bayirli GS. Evaluation of the root canal configurations of the mandibular and maxillary permanent teeth by gender in the Turkish population. J Endod 2004;30:391e8.

6. Rahimi S, Shahi S, Yavari HR, Manafi H, Eskandarzadeh N. Root canal configuration of mandibular first and second premolars in an Iranian population. J Dent Res Dent Clin Dent Prospects 2007;1:59e64.

7. Awawdeh LA, Al-Qudah AA. Root form and canal morphology of mandibular premolars in a Jordanian population. Int Endod J 2008;41:240e8.

8. Velmurugan N, Sandhya R. Root canal morphology of mandib-ular first premolars in an Indian population: a laboratory study. Int Endod J 2009;42:54e8.

9. Jain A, Bahuguna R. Root canal morphology of mandibular first premolar in a gujarati populationdan in vitro study. Dent Res J (Isfahan) 2011;8:118e22.

10. Baisden MK, Kulild JC, Weller RN. Root canal configuration of the mandibular first premolar. J Endod 1992;18:505e8. 11. Khedmat S, Assadian H, Saravani AA. Root canal morphology of

the mandibular first premolars in an Iranian population using cross-sections and radiography. J Endod 2010;36:214e7. 12. Sikri VK, Sikrif P. Mandibular premolars: aberrations in pulp

space morphology. Indian J Dent Res 1994;5:9e14.

13. Sandhya R, Velmurugan N, Kandaswamy D. Assessment of root canal morphology of mandibular first premolars in the Indian population using spiral computed tomography: an in vitro study. Indian J Dent Res 2010;21:169e73.

14. Liu N, Li X, Liu N, Ye L, An J, Nie X, et al. A micro-computed tomography study of the root canal morphology of the mandibular first premolar in a population from southwestern China. Clin Oral Investig 2013;17:999e1007.

15. Liao Q, Han JL, Xu X. Analysis of canal morphology of

mandibular first premolar. Shanghai Kou Qiang Yi Xue 2011;20: 517e21 [Article in Chinese].

16. Yu X, Guo B, Li KZ, Zhang R, Tian YY, Wang H, et al. Cone-beam computed tomography study of root and canal morphology of mandibular premolars in a western Chinese population. BMC Med Imaging 2012;12:18.

17. Yang H, Tian C, Li G, Yang L, Han X, Wang Y. A cone-beam computed tomography study of the root canal morphology of mandibular first premolars and the location of root canal ori-fices and apical foramina in a Chinese subpopulation. J Endod 2013;39:435e8.

18. Neelakantan P, Subbarao C, Ahuja R, Subbarao CV,

Gutmann JL. Cone-beam computed tomography study of root and canal morphology of maxillary first and second molars in an Indian population. J Endod 2010;36:1622e7.

19. Scarfe WC, Levin MD, Gane D, Farman AG. Use of cone-beam computed tomography in endodontics. Int J Dent 2009;2009: 634567.

20. Plotino G, Tocci L, Grande NM, Testarelli L, Messineo D, Ciotti M, et al. Symmetry of root and root canal morphology of maxillary and mandibular molars in a white population: a cone-beam computed tomography study in vivo. J Endod 2013;39: 1545e8.

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